The present invention relates to projectiles of the type which disperse a quantity of fluent or powdered substance on impact. Such projectiles are used for the purpose of marking points of impact in training exercises, but may also be used in combat to disperse smoke, anti-personnel chemicals, and the like. The simplest approach to designing a projectile for this purpose is to enclose the spotting powder or other substance in a frangible case that bursts open when it strikes. However, this throws the powder forwardly on the ground, and the point of impact is not easily seen from a distance, especially on rolling or broken terrain. It is preferable to expel the powder upwardly and to the rear, to form a cloud extending some height above the ground.
One known method for doing this is to arrange an explosive cartridge and a container of spotting chemical in the projectile in such fashion that a nose impact blows the chemical out of a tube open to the rear. This is suitable for a large practice projectile such as a bomb or a large caliber shell in which space is not at a premium, and where the additional cost of the explosive cartridge and an impact-actuated firing pin mechanism may not be objectionable, but is not well adapted to small shells or grenades.
Still another known proposal has been to form the projectile of inner and outer telescoping members, of which the inner one is forced rearwardly at impact to compress a liquid container against a rear portion of the outer one, breaking the container and expelling the liquid through nozzles at the rear of the projectile. Apart from the cost of machining this complex device, the use of nozzles is not well suited to the ejection of particulate solid material, even if finely powdered. Further, since the telescoping stroke continues only during the interval between impact and arrest of the inner and outer members, an impact on soft earth or sand might not stop the inner member until the outer member had already made contact with the surface, so that the full stroke might not take place. This would be all the more probable because it is necessary to connect the inner and outer members by a detent strong enough to prevent relative motion during firing, and this must be broken by absorbing a large part of the impact energy before the telescoping stroke can begin.
The general object of the present invention is to increase the visibility of a spotting projectile by improving the dispersion of fluent or powdered materials from the projectile. Another object is to provide an improved spotting projectile which is less complex and expensive to produce than prior projectiles of which I am aware, and which is reusable. Further objects and advantages will appear as the following description proceeds.
Briefly stated, according to preferred embodiments thereof, I carry out my invention in part by forming a projectile casing with a longitudinal interior passage, preferably cylindrical in shape, which opens rearwardly to the exterior, but terminates forwardly in an enclosing wall behind the nose of the projectile. A piston is conformably and slidably received in gas-sealing relation within this passage to form an expansible chamber. The piston carries a quantity of spotting medium, which may for example comprise fluidized talcum powder or the like, with or without the addition of a fluorescent material.
In a preferred form, the piston includes a tubular sleeve member slidable in the casing passage, and a container for the spotting medium received conformably within the tubular member. The piston is initially located at the rear of the passage, where it rests against a cap which encloses the rear passage opening and is temporarily held on the casing by a weak cement, adhesive tape, or other suitable means. A pusher wad encloses the cap and the rear end of the casing, holding the cap and piston securely in place on the projectile as it is accelerated in the firearm barrel. The wad separates from the projectile, preferably shortly after it leaves the muzzle of the firearm; the cap remains in place during flight, but is knocked off by the impact of the projectile as it lands. The spotting-medium container is enclosed rearwardly by a frangible diaphragm, which may for example be formed of adhesive plastic tape, and is designed to burst open on impact.
As the projectile lands and instantly decelerates, the inertia of the piston drives it forcefully forward, compressing the air or gaseous medium in the interior passage. When the piston has decelerated, the container is expelled by the gas pressure through the rear opening of the casing, spewing the spotting medium out in a cloud. As the projectile generally lands with its nose inclined downwardly, this projects the cloud upwardly so that it becomes plainly visible from a considerable distance.